c ++将类转换为布尔值
对于 C++ 的所有基本类型，可以简单地查询:
With all of the fundamental types of C++, one can simply query:
if(varname)
并且类型被转换为布尔值以进行评估.有没有办法在用户定义的类中复制这个功能?我的一个类由一个整数标识，尽管它有许多其他成员，我希望能够检查整数是否以这种方式设置为 NULL.
and the type is converted to a boolean for evaluation. Is there any way to replicate this functionality in a user-defined class? One of my classes is identified by an integer, although it has a number of other members, and I'd like to be able to check if the integer is set to NULL in such a manner.
谢谢.
推荐答案
您可以定义一个用户定义的转换运算符.这必须是成员函数，例如:
You can define a user-defined conversion operator. This must be a member function, e.g.:
class MyClass {
operator int() const
{ return your_number; }
// other fields
};
您还可以实现运算符 bool.但是，我会强烈建议不要这样做，因为您的课程将变得可用于算术表达式，这会很快导致混乱.例如，IOStream 定义转换为 void*.您可以像测试 bool 一样测试 void*，但没有来自 void* 的语言定义的隐式转换.另一种选择是使用所需的语义定义 operator!.
You can also implement operator bool. However, I would STRONGLY suggest against doing it because your class will become usable in arithmetic expressions which can quickly lead to a mess. IOStreams define, for example, conversion to void*. You can test void* in the same way you can test a bool, but there are no language-defined implicit conversions from void*. Another alternative is to define operator! with the desired semantics.
简而言之:定义转换运算符 sto 整数类型(包括布尔值)是一个非常糟糕的主意.
In short: defining conversion operator sto integer types (including booleans) is a REALLY bad idea.
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